1. Field of the Invention
The present invention relates to apparatus and methods for non-intrusive measurements of internal pressure and/or other measurements and, more specifically, to hoop-mode and bending-mode resonance vibration of a tubular section for determining internal pressure and/or other measurements such as those produced by Coriolis mass flow meters.
2. Description of Prior Art
Traditional measurements of gas pressure in a plumbing system typically require penetration through a vessel wall to provide a coupling or pressure port from the enclosed gas to the transducer's sensing surface. The pressure port is connected to a fluid-coupled sensor such as a pressure responsive diaphragm. In some systems, it is desirable to provide a non-intrusive pressure sensor whereby it is meant that no sensor surface other than a section of containment conduit such as steel pipe is in contact with the fluid so that it is not necessary to penetrate an existing wall to contact a diaphragm. Moreover, a non-intrusive sensor as disclosed herein preferably permits fluid to flow therethrough in an unrestricted manner through a section of pipe and can be retrofitted to the plumbing of a system by addition of the section of pipe. As far as could be determined, non-intrusive pressure sensors are not available from commercial vendors.
While a non-intrusive pressure measurement system may be useful for various applications, a particular application of interest is that of monitoring the health of propulsion system components such as the Helium Pressurization Components of the Space Shuttle's Orbital Maneuvering System and Reaction Control System. Thus, there is also a desire to measure pressures of specific gases and therefore for determining whether different gases may cause a difference in the response of a vibrational pressure measuring device irrespective of gas pressure.
Coriolis flow measurement devices are commercially available for measuring liquid flow and, more recently, gas flow. The physical operating principle in such meters is based on a Coriolis acceleration. In some cases, these devices are also used to measure gas density and temperature. The presently available Coriolis flow measurement devices fall into two general categories according to the vibrational mode used in the sensing pipes, i.e., hoop-mode and bending-mode implementations. There are many bending-mode implementation variations with respect to the shape of the bend and the location of the sensors some of which variations are discussed in some of the following listed patents. The operation of Coriolis type flow measurement is based on a Coriolis acceleration of the fluid mass within a pipe section and results in a measurable deflection. The deflection is directly proportional to mass flow through the tube. While rotational motion may be used to implement a Coriolis type flow meter, vibration may also be used to produce the same Coriolis force. The bending mode implementation for a Coriolis flow meter utilizes a vibration mode for which a curved segment of pipe is cantilevered about the axis of an adjacent straight section. Sensors on each of the two legs of the vibrated U-hoop or bent pipe sense the difference in phase of the two legs resulting from the twist caused by the constrained fluid segment. This relative phase difference is the physical operating principle of the bending-mode Coriolis mass flow meter. The hoop-mode implementation for a Coriolis flow meter utilizes a vibration mode for which a narrow cross-section of a straight section of pipe is vibrationally squeezed such as by a driving element that may be a piezoelectric element or other driver element. The pinching vibration causes a slight deflection velocity that is detected by another sensor which for certain modes of vibration may be located at the diametrically opposite side from the driver element. Physical parameters sensed in the commercial Coriolis-type meters include the phase shift between axially displaced sensors, the frequency or period of the vibrated pipe segment, and the pipe temperature. Numerous implementations have demonstrated that the mass flow rate for these meters is proportional to the phase shift between appropriately located sensors on the vibrated pipe carrying the process fluid. The frequency of the vibrating pipe segment, usually driven at resonance or slightly off resonance, is typically measured to calculate the density of the gas and to compensate the density dependence of the flow measurement. The temperature of the pipe is typically measured to provide temperature compensation for the elastic coefficient of the tube, but that temperature is also often taken to be a satisfactory approximation for the temperature of the fluid. This latter approximation is typically close for most fluids but becomes increasingly poorer with decreasing fluid density.
N. M. Keita discloses a theoretical and measured pressure effect on meter characteristics of frequency and mass flow sensitivity for constant fluid density in "Behavior of Straight Pipe Coriolis Mass Flowmeters in the Metering of Gas: Theoretical Predictions with Experimental Verification" from Flow Measurement and Instrumentation, Vol. 5, No. 4 (1994): pp. 289-294. However, Keita states that the pressure effect (on mass flow sensitivity error) is due to stress stiffening of the mechanical oscillator, is strongly dependent on design, and is not easy to compute. Possibly for this reason Keita's goal is to provide corrections for mass flow rate measurement rather than determine pressure directly.
U.S. Pat. No. 4,600,855, issued Jul. 15, 1986, to J. S. Strachan, discloses an apparatus for measuring pressure within a conduit whose resonant frequency varies with the pressure of the fluid within the tube. As shown, the device requires insertion into the pressure media to be measured, i.e., blood artery pressure, and is therefore an intrusive type of pressure sensor rather than a non-intrusive sensor. The device is not intended to be used with gas or with flowing fluid. The axial length of the sensors limits sensitivity of the device and, due to multiple modes of vibration, would probably not be operable when used when fluid flows therethrough. The disclosed range of measurable pressures is not adequate for certain operations. Excitation means are not disclosed. Other types of measurements are not disclosed. Bending mode and, effectively, hoop-mode operation are not disclosed.
U.S. Pat. No. 5,585,567, issued Dec. 17, 1996, to P. Van Manen discloses an apparatus for exciting at least the fundamental radial circumferential mode of vibration and the first harmonic thereof in a gas bottle. Both frequencies are used for determining the pressure of the bottle. The device is apparently not intended to be particularly accurate as the inventor states that the need is to quickly determine whether a gas bottle is pressurized or not where the bottles are often stacked closely together.
U.S. Pat. No. 3,021,711, issued Feb. 20, 1962, to G. Arvidson, discloses an intrusive-type pressure sensor, with the pressure coupled to a sensing device within a housing rather than a pipe section through which fluid can freely flow. The invention is characterized by the provision of a hollow body capable of being set in vibration by feeding energy thereto. The respective pressure or difference pressure is supplied to the device through one or two openings within a housing to allow a pressure or difference pressure between two fluids to be measured.
U.S. Pat. No. 3,257,850, issued Jun. 28, 1966, to R. R. Kooiman, discloses an intrusive type of sensor which in the tubular form thereof uses a flexible diaphragm for detecting pressure vibration.
U.S. Pat. No. 4,098,133, issued Jul. 4, 1978, to Frische et al., discloses an intrusive fluid pressure type having a thin flat vibrating diaphragm serving as a wall of a continuous pressure chamber for converting a variable fluid pressure magnitude directly into a variable frequency electrical signal.
U.S. Pat. No. 5,528,939, issued Jun. 25, 1996, to Martin et al., discloses an improved gas pressure gauge that extends the linear range of pressure dependent damping to higher pressures by placing a stationary member in very close proximity to the vibrating member.
U.S. Pat. No. 5,249,467, issued Oct. 5, 1993, to M. Takashima, discloses a vascular pressure detecting apparatus with a pressure sensor having a vibrating element forming a pressure sensing surface which is secured to a housing at the periphery end thereof.
U.S. Pat. No. 4,991,153, issued Feb. 5, 1991, to Tsuruoka et al., discloses a device that detects the resonant frequency of a vibratory member in contact with a fluid.
U.S. Pat. No. 4,691,573, issued Sep. 8, 1987, to Varnum et al., discloses a fluid filled force or pressure sensor for measuring an external force such as fluid pressure using a flexible diaphragm in contact with the fluid of interest.
U.S. Pat. No. 4,872,335, issued Oct. 10, 1989, to Tsuruoka et. al, discloses a vibrating transducer for detecting the resonant frequency of a vibrating diaphragm and using that frequency to determine the pressure or density of a fluid contacting the diaphragm.
U.S. Pat. No. 4,644,796, issued Feb. 24, 1987, to Roger W. Ward, discloses a fluid density measuring apparatus and method for directly measuring fluid density or indirectly measuring pressure using a bellows.
U.S. Pat. No. 4,385,636, issued May 31, 1983, to E. R. Cosman, discloses an improvement in design of an implantable telemetric differential pressure sensing device.
U.S. Pat. No. 4,574,639, issued Mar. 11, 1986, to R. W. Ward, discloses a fluid density measuring apparatus and method for directly measuring fluid density or indirectly measuring pressure, temperature, acceleration, flow velocity, differential pressure and other parameters affecting the apparatus by using a bellows apparatus and other sensor elements.
U.S. Pat. No. 4,563,902, issued Jan. 14, 1986, to R. Kohnlechner, discloses a pressure measuring device wherein a housing includes a pressure sensor in a pressure chamber and an electronic circuit in a non-pressurized chamber.
U.S. Pat. No. 4,126,049, issued Nov. 21, 1978, to M. A. Cotter, discloses a system and method for measuring fluid pressure based on resonant frequency of a nearly perfect single crystal material.
U.S. Pat. No. 5,373,745, issued Dec. 20, 1994, to D. R. Cage, discloses a flow meter apparatus for measuring the mass flow rate of a fluid using the Coriolis principle. In one aspect, it is apparently taught that pressure may be derived from equations containing two frequency modes rather than a single resonant frequency.
U.S. Pat. No. 5,423,225, issued Jun. 13, 1995, to D. R. Cage, discloses a flow meter apparatus for measuring the mass flow rate of a fluid using the Coriolis principle.
U.S. Pat. No. 5,448,921, issued Sep. 12, 1995, to Cage et al., discloses teachings similar to those in the above cited references for which he is listed as an inventor.
U.S. Pat. No. 5,837,885, issued Nov. 17, 1998, to Goodbread et al., discloses a resonator vibrating close to its resonance frequency excited by a first transducer and connected to an oscillator. The vibration is measured by the transducer or a second transducer and stabilized by a phase-lock feedback loop. No teaching is made of how to determine pressure. As well, the control system apparently is not designed to maintain a system at resonance frequency. Moreover it is not disclosed how to do so with minimum phase shift error as may be desirable for measuring pressure especially with mass flow.
U.S. Pat. No. 5,656,779, issued Aug. 12, 1997, to A. J. Bronowicki, discloses a self-exciting vibratory device for producing vibration signals in a housing and includes an actuator means, sensor means, and electronics module.
U.S. Pat. No. 5,235,844, issued Aug. 17, 1993, to Bonne et al., discloses a transducer apparatus using tuning forks for simultaneously determining pressure and one other property of a flowing gas of varying pressure and composition.
U.S. Pat. No. 5,675,074, issued Oct. 7, 1997, to R. G. Melvin, II., discloses a method of analyzing internal pressure of a closed container including vibration of a surface, detecting sound resulting from the detected sound, and determining whether the information corresponds to predetermined spectral frequency condition. No effort to vibrate a tube at resonance is disclosed.
U.S. Pat. No. 5,353,631, issued Oct. 11, 1994, to Woringer et al., discloses that the internal pressure of a sealed container is characterized by tapping to vibrate a wall of the container and then basing the characterization of the internal pressure on a frequency spectrum of the vibration and stored data measured from vibrating other containers.
U.S. Pat. No. 5,351,527, issued Oct. 4, 1994, to Blackburn et al., discloses an apparatus for sensing pressure in a stiff wall sealed vessel that comprises high pressure gas for inflating a car air bag that establishes oscillations of the pressurized fluid in the vessel and detects roughly whether the pressure level is too low. The device does not teach flow measurement.
U.S. Pat. No. 4,869,097, issued Sep. 26, 1989, to Tittmann et al., discloses an apparatus for measuring the pressure of a gas within a sealed vessel. A sonic transducer is used to apply an oscillating force to the surface of the vessel. The frequency of the ultrasonic wave is swept through a range which causes resonant vibration of the gas.
U.S. Pat. No. 4,838,084, issued Jun. 13, 1989, to Leopold et al., discloses a density measurement that measures the density of a fluid by determining the frequency of oscillation of a vibrating tube filled with the fluid.
U.S. Pat. No. 5,386,714, issued Feb. 7, 1995, to A. N. Dames, discloses a density sensor that comprises a cavity arranged to receive the gas whose density is to be sensed. The cavity is divided into two chambers by a flexibly mounted diaphragm.
U.S. Pat. No. 4,604,898, issued Aug. 12, 1986, to Gohin et al., discloses a circuit using the properties of a resonating cavity sensor whose resonance frequency is modified by the electric capacity variations due to the mechanical deformation of a wall under the effect of the pressure to be measured.
U.S. Pat. No. 4,187,718, issued Feb. 12, 1980, to K. Shibasaki, discloses an apparatus for inspecting the internal pressure of a hermetically sealed container wherein a sound wave of free damped oscillation excited at the elastic wall of a hermetically sealed container is converted and detected as an electrical signal.
U.S. Pat. No. 4,009,616, issued Mar. 1, 1977, to J. W. Wonn, discloses a nondestructive acoustic method for measuring gas pressure in a hermetically sealed enclosure. The acoustic impedance mismatch between the enclosure and the gas medium is dependent upon the pressure of the gas and correspondingly affects the transmissivity of the acoustic signal.
U.S. Pat. No. 3,802,252, issued Apr. 9, 1974, to G. G. Hayward, discloses an apparatus for monitoring the pressure in a sealed container. The frequency spectrum of the signal output of the pickup device is examined. The signal output is gated.
The above discussed patents do not disclose a non-intrusive pressure sensor that requires only connecting a steel pipe section to the system plumbing and through which flow may occur. It is desirable that no sensor surface other than the steel pipe section be in contact with the fluid. Moreover, it is desirable to be able to measure pressure as fluid flow occurs and, preferably, to measure the fluid flow rate and fluid density simultaneously with pressure. A review of the above references reveals that a long felt need exists for apparatus and methods for providing non-intrusive pressure measurements. It would be desirable to have a sensor that is readily attachable or easily built into the system without adding obstructions, diaphragm ports, and the like. Those skilled in the art have long sought and will appreciate the present invention that addresses these and other problems.